Process for lining high pressure pipeline

ABSTRACT

A method for lining a high pressure pipeline with a tubular plastic liner. After depressurizing, purging and cleaning the pipeline is broken into discrete sections each of which is to receive a liner segment. The sections are reamed to remove obstructions which might damage the liner and a close-fitting liner segment is drawn into each section. Each liner segment is fixed at opposed ends of respective pipeline sections to prevent longitudinal movement of the segments. Bleeder holes are provided through the pipeline walls at opposed ends of each pipeline section. After the pipeline sections are reconnected to reform the pipeline, a relatively warm, pressurized fluid is pumped through the pipeline to radially expand each liner segment against the inner walls of the pipeline, thus evacuating the spaces between liner segments and pipeline sections by forcing air, water and other impurities through the bleeder holes.

This is a continuation-in-part of application Ser. No. 115,488 filedJan. 25, 1980 and now abandoned.

FIELD OF THE INVENTION

This invention relates to methods for lining pipelines, and, inparticular, to a method for lining a buried high pressure pipeline.

BACKGROUND OF THE INVENTION

It is known to provide a loose-fitting plastic liner to extend the lifeof an existing low pressure pipeline. (By "low pressure" it is meantthat pressures inside the pipeline do not exceed about 150 pounds persquare inch ["psi"] when the pipeline is in service.) However, plasticliners are not used in high pressure pipelines such as water injectionlines where pressures of 5,000 psi or more may be encountered inside thepipeline. The reason for this is that in conventional "relining"applications, the existing pipeline is used simply as a "guide" toreceive a loose-fitting tubular plastic insert. The loose-fittinginsert, once installed in the pipeline, serves as a new "pipeline"--theinsert conveys the material formerly conveyed by the pipeline, but, inso doing, must be capable of withstanding whatever pressures may berequired to transport the material there-through. Such loose-fittingplastic inserts are unsuitable for use in high pressure pipelinesbecause they are not capable of withstanding the strain encountered whenthe interior region of the liner is pressurized, forcing the liner toexpand radially toward the internal walls of the pipeline. Viewed inthis light, it becomes apparent that, strictly speaking, the use of aloose-fitting insert is not properly described as "pipeline relining"because the insert does not serve as a "liner" but serves instead as anew pipeline having a somewhat smaller outside diameter than the insidediameter of the existing pipeline, there being an annular gap betweenthe outer wall of the plastic insert and the inner wall of the existingpipeline.

The present invention, by contrast, provides a close-fitting liner.After completion of the procedure hereinafter described, the liner isdisposed inside the pipeline with no annular gap between the liner andthe pipeline. Because the liner contacts the inner walls of thepipeline, the liner itself need not be capable of withstanding thepressures encountered inside the pipeline.

Loose-fitting plastic inserts are conventionally installed in pipelinesin an effort to extend the piping system life at a cost somewhat lowerthan that of installing a new pipeline. Loose-fitting plastic insertsare sometimes also intended to protect an existing pipeline againstinternal corrosion or abrasion. The installation of a loose-fittingplastic insert into a pipeline may also improve the flow characteristicsof the pipeline beyond those observed in a similar pipeline which is notequipped with a loose-fitting plastic insert. Loose-fitting plasticinserts may also eliminate, or at least reduce the need to use oxygenscavengers, rust inhibitors or other chemicals to maintain the pipeline.The present invention, while providing these and other advantages,provides the further advantage that it is not restricted to use in lowpressure applications but may be used in applications where internalpipeline pressures of several thousand psi are encountered.

Accordingly, it is an object of the present invention to provide amethod of lining a pipeline with a plastic liner such that the linedpipeline is capable of withstanding internal pressures in excess ofthose which the liner alone could withstand.

A further object is to provide such a method which is relativelyinexpensive, when compared with the cost of installing a new pipeline,and which is relatively easy to implement.

SUMMARY OF THE INVENTION

The invention provides a method of lining a section of a high pressurepipeline which utilizes the structural strength of the pipeline toenable the lined pipeline section to be operated at high pressure. Thepipeline section includes first and second flanges disposed at oppositeends thereof. The method comprises the steps of:

(a) providing a firm plastic liner having:

(i) a wall thickness such that the liner is form-sustaining;

(ii) an outside diameter sufficiently less than the inside diameter ofthe pipeline to enable drawing the liner through the pipeline section,but sufficiently large so that the liner can be non-destructivelyradially expanded against the inside wall of the pipeline;

(b) drawing the liner into the pipeline section until the liner issubstantially longitudinally co-extensive with the pipeline section;

(c) longitudinally stretching the liner within the section;

(d) fixing the liner against longitudinal movement within the section;

(e) opening at least one bleeding port in the section;

(f) radially expanding the liner against the inside wall of the pipelineto an extent to permanently change the liner outside diameter from itsoriginal size to a size conforming to the inside diameter of thepipeline;

(g) during step (f), bleeding the space between the liner and thepipeline through the bleeding port; and,

(h) closing the bleeding port.

Preferably, the liner is radially expanded by no more than 6% of itsoriginal diameter. Advantageously, the radially expanding step comprisesapplying to the liner a relatively warm fluid under relatively lowpressure. The fluid may have a temperature of about 180 degrees F. and apressure of not more than about 100 psi.

The liner is fixed in the pipeline section by the following steps:

(a) before the drawing step, affixing a first flange to an end of theliner segment;

(b) after the drawing step, positioning the first liner flange againstthe first pipeline section flange;

(c) after the stretching step, affixing a second flange to the end ofthe liner segment opposite the first liner flange; and,

(d) positioning the second liner flange against the second pipelineflange.

Advantageously, before the radially expanding step, the liner flangesare encircled with retaining rings.

DRAWINGS

FIG. 1 is a perspective view of an end of a pipeline section having aflange affixed thereto;

FIG. 2 is a perspective view of a cable-carrying pig;

FIG. 3 is a fragmentary plan view of a pig launching device coupled to apipeline section;

FIG. 4 is a fragmentary perspective view of a pulling head affixed to aliner segment;

FIG. 5 is a fragmentary perspective view of an alternate pullingarrangement affixed to a liner segment;

FIG. 6 is a fragmentary perspective view of a further alternate pullingarrangement affixed to a liner segment;

FIG. 7 is a perspective view of an excavation site showing a partiallyexposed portion of a pipeline section into which a liner segment isabout to be pulled;

FIG. 8 is a perspective view showing a further alternate arrangement forpulling a liner segment;

FIG. 9 is a fragmentary perspective view of a liner segment having aplastic flange affixed thereto;

FIG. 10 is a cross-sectional view, on a slightly enlarged scale, of theplastic flange of FIG. 9;

FIG. 11 is a perspective view showing the clamping against longitudinalmovement of a liner segment which has been drawn through a pipelinesection;

FIG. 12 is a perspective view of a retaining ring for use with theplastic flange of FIGS. 9 & 10;

FIG. 13 is a sectional view showing the installation of the retainingring of FIG. 12.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The following description will make particular reference to theinsertion of a plastic liner into a pipeline which is buried in situ. Itis to be understood however, that the method is of general applicationand may be used with pipelines or pipeline sections which are notburied.

SITE PREPARATION

Before commencing installation of a liner into a pipeline, the right ofway along the pipeline route should be examined to determine suitablepoints at which the pipeline may be uncovered and broken to create aplurality of pipeline sections, each of which sections is to receive anindividual liner segment. Typically, for the preferred liner materialreferred to hereinafter, the pipeline will be broken about every 2,000feet. It is recommended that pipeline sections not exceed about 2,500feet in length because the tensile yield point of the liner materialmight be exceeded and the liner consequently damaged if the linersegment is subjected to the force necessary to pull it through apipeline section over such a distance. Otherwise, the length ofparticular pipeline sections is not particularly critical and may bevaried to accommodate conditions along the pipeline right of way so asto avoid swamp areas, roads, rail crossings, etc. The length ofindividual pipeline sections may also be limited by the availability ofwinch equipment of a capacity sufficient to exert the force necessary topull a liner segment of a given length through a pipeline section.

Before work commences, the pipeline should be de-pressurized, purged,and cleaned if necessary.

LINER MATERIAL

The preferred liner material is polyethylene plastic in a firm, tubular,form-sustaining configuration (i.e. plastic pipe) which may befield-assembled into segments up to 2500 feet in length and which canwithstand a radial expansion of at least 6% without cracks developingfor at least one year. The liner material should have an environmentalstress crack resistance (E.S.C.R.) rating in excess of 1000 hours whentested in accordance with conditions A, B and C of ASTM test D-1693-75.Ultra High Molecular Weight High Density Polyethylene ("UHMWHDP") whichmeets Plastic Pipe Institute designation P.E. 3406 is especiallypreferred for use as the liner material. An acceptable liner material ismanufactured by Phillips Products Co., Inc. under the trade markDriscopipe 8600.

LINER OUTSIDE DIAMETER

The outside diameter of the liner material must be carefully selected asa function of the inside diameter of the pipeline. If the outsidediameter of the liner material is too large, then it may not be possibleto pull a liner segment through a pipeline section without subjectingthe liner segment to forces so great that it is ruptured. On the otherhand, if the outside diameter of the liner material is too small, thenthe liner may be ruptured when it is radially expanded inside thepipeline as hereinafter described.

Tests indicate that UHMWHDP in tubular form may be expanded radially bya factor of about 12% to 15% before rupture occurs. As a safety measure,these factors are halved in an effort to ensure that the liner materialis not ruptured when radially expanded to contact the internal pipelinewall. Preferably, the liner material is radially expanded by a factor ofno more than 6% of its original diameter. If radial expansion of theliner material is limited in this manner, there will be minimal riskthat factors such as irregularities in the inside diameter of the linermaterial, or surface damage caused in pulling a liner segment into aparticular pipeline section will result in rupture of the liner.

As a practical matter, the following table illustrates outside diametersof UHMWHDP liner materials which have proved acceptable in fieldapplications:

    ______________________________________                                                        Liner Material Outside                                                        Diameter as a % of                                            Pipeline Inside Diameter                                                                      Pipeline Inside Diameter                                      ______________________________________                                        2" to 3"        94%                                                           4"              95%                                                           6" to 8"        96%                                                           10" and above   96.5% to 97.5%                                                ______________________________________                                    

The closer tolerance used with larger diameter pipelines represents adecrease in deformation of the liner material as it is radially expandedto contact the inside wall of the pipeliner with a commensurate decreasein probability that the liner material will rupture.

LINER WALL THICKNESS

The wall thickness of the liner material will be governed by a number ofconsiderations.

To some extent, expense will govern the liner material wall thickness.Suppliers of liner material have reported that considerable cost isinvolved in retooling to produce a liner material of a given wallthickness. A further complication faced by suppliers of liner materialis that, as mentioned above, the outside diameter of the liner materialmust be carefully selected where it is desired to insert a close-fittingliner into a pipeline. Ideally, both the outside diameter and the wallthickness of the liner material are individually matched to a givenapplication. Usually, however, the expense involved in individuallymatching both parameters dictates a practical compromise in which theoutside diameter of the liner material is carefully selected with anattendant sacrifice in wall thickness dimension. For example, the linermaterial supplier may use a die which is capable of producing a tubularplastic material having a standard outside diameter and a standard wallthickness, but adjust his production method to vary the outside diameterof the liner material as required, which may result in an increase or adecrease in the wall thickness of the liner material.

A further factor governing liner material wall thickness arises becausethe liner material is usually supplied in relatively short lengths whichare heat fused together at the pipeline relining site to produce linersegments up to 2500 feet in length for insertion into particularpipeline sections. The wall thickness of the liner material will, tosome extent, affect the quality of the joints at which the lengths ofliner material are heat fused. For example, a liner material having anexceptionally thin wall would be difficult to heat fuse because the endsof the material would tend to assume an oval shape when clamped andheated in a conventional fusion joining machine. Practical fieldexperience suggests that the liner material wall thickness should not beless than about 0.13 inches to prevent this problem. Preferably, thewall thickness of the liner material is greater than about 0.2 inches sothat the original tubular form of the liner may be sustained while linersegments are heat fused together.

In some applications the fluids to be transported through the linedpipeline may abrade the liner material. Tests may be conducted todetermine the rate at which the liner material is abraded by aparticular fluid and then a liner wall thickness may be calculated byassuming a given desired lifetime for the liner material.

Each segment of liner material must be capable of withstanding theforces imposed on the segment when it is pulled into a given pipelinesection as hereinafter described, without stressing the liner materialbeyond its tensile yield point (the liner material tensile yield pointshould be obtainable from the liner material supplier). As the linermaterial wall thickness decreases, greater care must be exercised indrawing the liner segment into the pipeline section to avoid exceedingthe liner material tensile yield point and consequent damage to theliner segment.

The wall thickness of the liner material may also be determinative ofthe ability of the liner to resist collapse if the interior of the lineris ever subjected to vacuum. An approximation of the collapse pressure"P_(c) " (in pounds per square inch) may be obtained from the formula:

    P.sub.c =2E(t/D).sup.3 /(1-u.sup.2)

where:

E=stiffness modulus (in pounds per square inch) of the liner material(available from the manufacturer of the liner material)

t=liner material wall thickness (in inches)

D=outside diameter of liner material (in inches)

u=Poisson ratio (about 0.45 for UHMWHDP liner material).

The liner will tend to collapse if the collapse pressure is greater thanor equal to 1 atmosphere (14.5 pounds per square inch). The wallthickness required to sustain the original tubular form of the linermaterial and resist such collapse may therefore be calculated for aliner material of a given outside diameter.

As discussed hereinafter, the preferred installation procedure mayproduce a vacuum in the annular region between the outside wall of aliner segment and the inside wall of the pipeline section which containsthat liner segment. A vacuum in this annular region would tend to offseta vacuum inside the liner segment. The wall thickness of the linermaterial required to resist collapse due to internal vacuum could thenbe decreased somewhat to take advantage of the offsetting vacuumsurrounding the liner segment.

As a practical example, the following table summarizes the wallthickness of UHMWDP liners which have been used successfully inclose-fitting pipeline relining applications:

    ______________________________________                                                           UHMWHDP                                                    Pipeline                                                                              Pipeline   Liner Material                                                                            UHMWHDP                                        Outside Inside     Outside     Liner Material                                 Diameter                                                                              Diameter   Diameter    Wall Thickness                                 ______________________________________                                        12.750" 12.250"    11.60"      0.370"                                         10.750" 10.250"    9.70"       0.335"                                          6.625"  6.193"    5.90"       0.270"                                          4.500"  4.163"    3.83"       0.130"                                         ______________________________________                                    

PREPARATION OF LINER SEGMENTS AND PIPELINE SECTIONS

Liner segments may be assembled on-site using a conventional fusionjoining machine to fuse lengths of liner material together. The linersegments should be at least 20 feet longer than the respective pipelinesections into which they are to be inserted. The external bead ofpolyethylene which is created on the liner segment by the fusion joiningprocedure must be removed to leave a smooth surface which will notimpede passage of the liner segment through the pipeline section orinterfere with radial expansion of the liner as hereinafter described.An "external bead trimmer" satisfactory for this purpose may be obtainedfrom McElroy Equipment of Tulsa, Okla. Since significant strain will beimposed on the fused joints during the stretching step hereinafterdescribed, extreme care should be used to avoid defects in the fusedjoints.

A plastic flange 86 is fused onto one end of each liner segment as apreparatory step (FIG. 9). FIG. 10 is a cross-section view of a plasticflange 86 which provides details of the construction of an acceptableflange. In FIG. 10:

D₁ =Diameter of raised outer face of pipeline flange 12.

D₂ =Inside diameter of pipeline.

D₃ =Inside diameter of liner material.

D₄ =Outisde diamater of liner material.

t₁ =Thickness of flange 86 (should be the greater of:

(i) thickness of a standard #150 polyethylene flange; or

(ii) twice the wall thickness of the liner material).

L₁ =a sufficient distance to ensure that the taper of flange 86 willrest inside the steel flange to steel pipe weld.

L₂ =greater than or equal to the width of the fusion joining machineholding clamp.

A first pipeline section is uncovered at opposed ends by excavating apair of "bell holes" along the pipeline right of way. A typical bellhole 100 is shown in FIG. 7. For ease of illustration, only one pipelinesection 10 is shown in FIG. 7. The pipeline, when initially uncovered,would of course extend through bell hole 100 from right to left.

The pipeline is severed in each bell hole, defining a discrete pipelinesection between the two bell holes. For smaller diameter pipelines (2 to4 inches) it will usually be convenient to uncover the pipeline forabout 50 to 100 feet on both sides of the bell hole so that opposingends of the pipeline in the bell hole may be manoeuvred away from oneanother for ease of working. Larger diameter pipelines are usually muchmore stiff and less manoeuvrable.

For a high pressure pipeline (typically steel) flanges 12 (FIGS. 1, 3and 11) are welded onto opposite ends of pipeline section 10 tofacilitate reforming of the pipeline when the pipeline sections havebeen lined.

Near each flange 12, a small "bleeder" hole (typically about 1/32 inchin diameter) is drilled through the wall of the pipeline. The purpose ofthe bleeder hole is described in more detail below. A threadlet 14 iswelded onto the pipe over the bleeder hole.

Flange 12 tapers into neck 18 (best seen in FIG. 3) which is butt-weldedonto the end of pipeline section 10. Care should be taken when weldingflange 12 onto pipeline section 10 to avoid excessive penetration ofweld bead into the cavity enclosed by pipeline section 10. Excessiveweld bead should be smoothed by grinding or filing to reduce thepossiblity that the liner will be damaged when it is pulled intopipeline section 10. Flange 12 has a raised circular apertured face 20,the inside diameter of the aperture being equal to the inside diameterof pipeline section 10. Flange 12 is conventional in the art, the onlymodification being the machining of a 6° radius on internal lip 22 offlange face 20. Lip 22 is machined to eliminate sharp edges which mightdamage the liner segment during insertion into pipeline section 10.

A cable-carrying device 30 (conventionally called a "pig") is shown inFIG. 2. Pig 30 comprises a central body member 32, having a pair ofcurved rubber cups 34 disposed at opposite ends. The external diameterof cups 34 is slightly greater than the internal diameter of thepipeline so that pig 30 may be tightly fitted inside pipeline section10. A pair of eyelets 36 are disposed at opposite ends of the pig bodymember. A cable is attached to an eyelet at one end of pig 30 and theopposite end of the pig inserted into pipeline section 10.

A "pig launching device" 40 (conventional in the art) is shown in FIG.3. Launching device 40 includes flange 42 which is coupled by means ofbolts 44 to flange 12. Plastic gasket 46 is disposed between flanges 12and 42 to effect a seal. The cable (which has been attached to pig 30,which now rests inside pipeline section 10 near flange 12) passesthrough aperture 48 at one end of the launching device 40. Waterinjection port 50 is coupled with a hose or other means to a water truckcapable of delivering water under pressure through the hose and intolaunching device 40. Pressurized water is thus forced through waterinjection port 50 and cavity 52 and thence into pipeline section 10behind pig 30 to propel pig 30 along pipeline section 10 with the cabletrailing behind. The cable (which may be coiled upon a reel) is drawnthrough aperture 48 as the pig passes through pipeline section 10.Suitable gasket means should be provided at aperture 48 to preventexcessive loss of water. A water pressure of about 100 psi to 150 psishould suffice to propel the pig and cable through about 2,000 feet ofpipeline.

In the absence of a source of pressurized water, compressed air couldalso be used to force the pig and cable through pipeline section 10.

When pig 30 and the attached cable emerge at the opposite end ofpipeline section 10, pig 30 is removed from the cable and replaced by a"pig train" and a test piece of the liner material. The cable is firstattached to a carbide steel headed "sizing" pig, having an outsidediameter slightly larger than the outside diameter of the liner segmentto be inserted into the pipeline section. Preferably, the outsidediameter of the sizing pig is about one half the sum of the outsidediameter of the liner material and the inside diameter of the pipeline.The sizing pig assists in determining whether the inside diameter of thepipeline section is too small to receive the liner segment. The secondpig in the pig train is a wire brush pig having a plurality of wirebristles for scraping built-up scale off the internal pipeline surface.The third pig in the pig train is a rubber-cupped cleaning pig used tocarry out of the pipeline section slag or scale broken off the pipelinewalls by the first two pigs. The pigs are provided with eye bolts andare connected together with steel cable. Finally, a 25 to 30 foot testsection of the liner material to be used in lining the pipeline isattached behind the pig train.

A winch is attached to the cable at the far end of the pipeline section.The pig train and test section of liner material are then pulled throughpipeline section 10 with the winch. Preferably, the winch is equippedwith a cable odometer so that the operator may determine the location ofpoints at which the pig train may become lodged in pipeline section 10.If the pig train cannot successfully be pulled through pipeline section10, then it will be necessary to uncover and open the pipeline at thepoint at which the pig train becomes lodged to effect repairs.

After the test section of liner material has passed through pipelinesection 10, it is examined for surface damage. If nicks, gouges, surfaceslits, etc., on the test section do not penetrate into the liner wall toa depth of more than about 10% of the liner wall thickness, then theliner segment may be safely inserted into the pipeline section. If thesurface nicks, gouges, surface slits, etc., penetrate into the linerwall to a depth of more than about 10% of the liner wall thickness, thenthe pipeline section must be repigged and cleaned to eliminate suchliner surface damage. (Preferably, the pipeline section is re-pigged andcleaned if the liner material is penetrated to a depth of more thanabout 0.04 inches, regardless of its wall thickness.)

Once the pipeline section has been pigged and cleaned to eliminateunacceptable liner surface damage, launching device 40 is again used topropel pig 30 and the cable back through pipeline section 10 so that thecable may be attached to liner segment 70 which is to be pulled intopipeline section 10. This procedure also gives pipeline section 10 awater flush to remove foreign matter.

PULLING LINER SEGMENT INTO PIPELINE SECTION

Various pulling arrangements which may be used to attach the cable toliner segment 70, are shown in FIGS. 4, 5, 6 and 8.

FIG. 4 shows a pulling head 60 having a generally tapered cylindricalconfiguration. Pulling head 60 may be fabricated from a solid piece ofpolyethylene, and a hole drilled therethrough to receive pin 62 to whicheyelet 64 is affixed. Pin 62 is anchored against longitudinal movementwith respect to pulling head 60 by means of washer 68 and bolt 66 whichis threadably received on the end of pin 62. Pulling head 60 is fusedonto the end of liner segment 70 opposite the end to which flange 86 isattached. Any protruding fusion bead is removed. The cable is thenattached to eyelet 64 and pulling head 60 is introduced into pipelinesection 10. Pulling head 60 is intended for use in high pressureapplications where it is desired to use a close-fitting liner segmenthaving an external diameter of at least 94% of the internal diameter ofpipeline section 10. In such close-fitting applications, it is importantthat pulling head 60 be free of protrusions which might impede transitthrough pipeline section 10.

The pulling arrangement shown in FIG. 5 comprises a plurality of metalstraps 72 spaced circumferentially around an end of liner segment 70 andbolted directly to the liner segment. Cable bridle 74 connects straps 72to the pulling cable. This arrangement may be used in lower presureapplications where the outside diameter of liner segment 70 may beconsiderably less than the inside diameter of pipeline section 10. Forexample, this arrangement could be used in lining a sewer line having a20 inch inside diameter with a polyethylene liner having an 18 inchoutside diameter.

The pulling arrangement shown in FIG. 6 may be used in lower pressureapplications where misalignment of joints in the pipeline may beencountered, or where foreign matter may have infiltrated into thepipeline section. Pulling head 76 comprises a plurality of metal strapscircumferentially spaced around an end of liner segment 70. The straps,which may be bolted to liner segment 70, protrude beyond the end ofliner segment 70, and are drawn together to form a cone having an eyelet78 at its apex. Reinforcing rings 80 add mechanical rigidity. Thepulling cable may be affixed to eyelet 78, and pulling head 76 drawnthrough pipeline section 10 to produce a ploughing action which maypermit the realignment of misaligned joints, and which may clear awaydebris which has accumulated in the pipeline section.

The pulling arrangement shown in FIG. 8 should be used only in lowerpressure applications to pull a short length of liner into a pipelinesection. This arrangement is primarily intended for pulling linersegments on the open pipeline right of way. A plurality of apertures 82are circumferentially spaced around an end of liner segment 70, and acable pulling bridle 84 passed through the apertures for affixation tothe pulling cable.

Referring to FIG. 7, a trench 102 is provided to assist in insertingliner segment 70 into pipeline section 10. The floor of the trenchshould be sloped from ground level down towards flange 12 at a ratio ofabout 5 horizontal to 1 vertical. Care should be taken to preventkinking of liner segment 70 as it is pulled into pipeline section 10.

In addition to the odometer mentioned previously, the winch apparatus(positioned at the end of pipeline section 10 opposite to that shown inFIG. 7) should be equipped with a cable weight indicator to permit theoperator to monitor the pulling force exerted on liner segment 70, andthus ensure that the tensile yield point of the liner material is notexceeded.

FIXING LINER SEGMENT INSIDE PIPELINE SECTION

Once liner segment 70 has been pulled into pipeline section 10, itshould be fixed against longitudinal movement with respect to pipelinesection 10 with the aid of a second plastic flange like that shown inFIGS. 9 & 10.

The cable winch is used as described above to pull liner segment 70 intopipeline section 10 until flange 86 contacts flange 12. Liner segment 70is then stretched by continuing to pull on liner segment 70 while flange86 contacts flange 12, care being taken however, not to exceed thetensile yield point of liner segment 70. A clamp 92 (FIG. 11) is thenaffixed around the end of liner segment 70 opposite to flange 86 at thepoint the liner segment protrudes from the pipeline section, to hold theliner segment against pipeline flange 12, thereby preventing linersegment 70 from retracting within pipeline section 10. Pulling head 60is then cut away from liner segment 70, and a second plastic flangeidentical to that shown in FIGS. 9 & 10 is fused onto the end of linersegment 70 which protrudes from pipeline section 10. Clamp 92 is thenremoved and liner segment 70 is allowed to retract inside pipelinesection 10 until the second plastic flange contacts pipeline flange 12.

A steel retaining ring 94 (FIG. 12) should be used to encircle theplastic flanges to prevent deformation thereof when the pipeline ispressurized. The inside diameter "A" of retaining ring 94 equals theoutside diameter of plastic flange face 90. The outside diameter "D" ofretaining ring 94, is sized such that retaining rig 94 will fit insidethe bolt circle pattern of flange 12.

When a pair of adjacent pipeline sections have been lined, thosesections are joined together using bolts 96 to couple opposing flanges12 as shown in FIG. 13. (Obviously, it is important that the bolt circlepatterns of opposing flanges 12 be aligned when the flanges are weldedonto adjoining ends of a pair of pipeline sections, so that the bolts 96will easily pass through both flanges.) Opposed plastic flange faces 90will be in sealing engagement between the steel flange faces 20. Thewidth dimension "B" of retaining ring 94 is sized to permit a tight sealbetween opposed faces 90 of plastic flanges 86 while preventing contactbetween the circumferential ends of retaining ring 94, and opposedflange faces 20.

Work proceeds in the above manner over the length of the pipeline. Thepipeline is uncovered at selected points to create pipeline sectionsinto which liner segments are drawn. The bell holes which serve as worksites at opposed ends of the various pipeline sections are left open asthe pipeline sections are lined.

RADIALLY EXPANDING LINER SEGMENTS

When liner segments have been inserted into all pipeline sections, andthe pipeline sections joined together to reform the pipeline, the linersegments may be radially expanded inside the pipeline sections.

Plugs 16 are first removed from threadlets 14 along the entire length ofthe pipeline. A relatively warm (typically about 180° F.) fluid such aswater or oil is then injected into one end of the lined pipeline andallowed to flow freely therethrough and emerge from the opposite endthereof. The warm fluid injection serves to commence radial expansion ofthe liner segments toward the inside walls of the pipeline sections. Thewarm fluid injection also serves to alter some mechanical properties ofthe liner material in an advantageous manner. For example, at warmertemperatures, thermoplastic materials such as UHMWHDP can sustain moredeformation before rupturing. Such materials also deform more quicklyunder constant stress as temperature increases. These twocharacteristics are prime considerations which suggest the selection ofthermoplastic materials such as UHMWHDP as a liner material and whichsuggest the injection of warm fluid into the lined pipeline to raise thetemperature of the liner material. To take full advantage of thesealterations in mechanical properties, all liner segments in the pipelineshould be at at least 70° F. before the pressure expanding stepdiscussed below is started. Preferably, warm fluid injection ismaintained until the pipeline itself is at least warm to the touch (70°F.-100° F.) at the end from which the injected fluid emerges.

The mere injection of warm fluid is not sufficient to expand the linersegments outward to contact the inside walls of the pipeline sections.Pressure must be applied to continue the radial expansion of the linersegments until they contact the inside walls of the pipeline sections.Ideally, the liner segments are expanded such that they retain theirexpanded configuration and remain in contact with the inside wall of thepipeline section after injection of the warm pressurized fluidterminates. When the temperature of all liner segments in the pipelinehas been raised to at least 70° F., the end of the pipeline from whichthe injected fluid emerges is blocked off. The injection of warm fluidat the opposite end of the pipeline is, however, continued. Thecontinued injection of warm fluid will exert pressure inside the linersegments, tending to expand the liner segments radially outward againstthe inside walls of the pipeline sections, thus evacuating the annularregions between the liner segments and the pipeline sections by forcingentrapped air and fluids out through the bleeder holes.

The pressure exerted inside the lined pipeline should be monitored andcontrolled so that it does not exceed about 100 psi. As this pressureincreases, a "plateau" will be observed at which pressure does notincrease as additional warm fluid is injected into the lined pipeline.The pressure inside the lined pipeline should be held relativelyconstant on the "plateau" to permit the liner segments to expandradially outward to contact the inside walls of the pipeline. At least20 minutes should be allowed for radial expansion of the liner segmentsout to the inside walls of the pipeline sections. Once the linersegments have contacted the inside walls of the pipeline, there will beobserved an increase in pressure above the "plateau" as more warm fluidis injected into the pipeline. Care should be taken to avoid injectionof substantial quantities of warm fluid into the lined pipeline beforeall liner segments have expanded out to contact the inside walls of thepipeline. Otherwise, localized stresses may develop on the linersegments, causing rupture of the liner.

As pressure inside the pipeline increases, "geysers" about 10 to 15 feethigh may be observed at the bleeder holes. This "geyser" effect willusually subside within about 20 to 30 minutes, although the bleederholes may continue to blow air for some considerable time thereafter.After a period of about 2 to 3 hours, there may be observed a drippingof a milky-white substance (believed to be emulsified air and water) atthe bleeder holes. At this point, the bulk of the air and waterentrapped between the liner segments and the inside walls of thepipeline sections will have been evacuated, and plugs 16 may be insertedinto threadlets 14 to close the bleeder holes. The pipeline may then besubjected to the usual tests required to satisfy the appropriateregulatory bodies.

In addition to expanding the liner segments within the pipelinesections, the radial expansion procedure will also indicate whetherparticular liner segments have been damaged during installation. If thewall of a particular liner segment has been pierced during installation,then the afore-mentioned "geyser" effect will not diminish at thebleeder holes of the pipeline section which contains that liner segment,due to the escape of pressurized fluid through the liner segment intothe annular region between the liner segment and the inside wall of thepipeline section. If such damage has occurred, then it will be necessaryto remove the defective liner segment, repig and reclean the particularpipeline section, install a new liner segment and then repeat theinjection of warm fluid and the pressure expansion step.

Evacuation of the annular region between respective liner segments andpipeline sections may serve a further useful purpose. If the pipelinehas to be shut down or depressurized such that a vacuum condition iscreated inside the liner segments, then, if plugs 16 have been insertedinto threadlets 14 to close the bleeder holes, an offsetting vacuumcondition should be present in the annular region surrounding each linersegment which may tend to prevent collapse of the liner segments due tothe vacuum inside the liner segments.

We claim:
 1. A method of lining a section of a high pressure pipelinewhich utilizes the structural strength of the pipeline to enable thelined pipeline section to be operated at high pressure, said sectionincluding first and second pipe flanges disposed at opposite endsthereof, the method comprising:(a) providing a plastic liner having:(i)a wall thickness and composition such that the liner is firm andself-sustaining in tubular form; (ii) an outside diameter sufficientlyless than the inside diameter of the pipeline to enable drawing theliner through the pipeline section, but sufficiently large so that theliner can be non-destructively radially expanded against the inside wallof the pipeline; (b) drawing the liner in non-collapsed condition intothe pipeline section by pulling the liner from one end area thereofthrough the pipeline section until the liner is substantiallylongitudinally co-extensive with the pipeline section; (c) beforeconcluding said drawing step, affixing a first liner flange to the endof said liner segment opposite said one end area; (d) completing thedrawing step to position said first liner flange against said first pipeflange; (e) longitudinally stretching the liner within the pipelinesection by elongating said liner without exceeding the elastic limit ofthe liner by pulling said one end area of the liner beyond the length ofthe pipeline section while said first liner flange prevents longitudinalmovement of the opposite end of said liner along the pipeline section;(f) after said stretching step, affixing a second liner flange to saidone end area of said liner segment opposite said first liner flange; (g)positioning said second liner flange against said second pipe flange bypermitting the liner to elastically retract into the pipeline section;(h) opening at least one bleeding port in the pipeline section; (i)radially expanding the liner against the inside wall of the pipeline toan extent to permanently change the liner outside diameter from itsoriginal size to a size conforming to the inside diameter of thepipeline; (j) during step (i), bleeding the space between the liner andthe pipeline through the bleeding port; and (k) closing the bleedingport.
 2. A method as defined in claim 1, wherein the liner is radiallyexpanded by no more than 6% of its original diameter.
 3. A method asdefined in claim 1, wherein said radially expanding step comprisesapplying to the interior of the liner a warm fluid under sufficientpressure to carry out the expansion.
 4. A method as defined in claim 3,wherein said fluid has a temperature of about 180 degrees F. and apressure of not more than about 100 psi.
 5. A method as defined in claim4, which further comprises, before said radially expanding step,encircling said liner flanges with retaining rings.
 6. A method asdefined in claim 1, which further comprises, before said drawing step,passing a short piece of liner material through the pipeline section todetect matter protruding into the space to be occupied by the liner. 7.A method as defined in claim 6, which further comprises, before saiddrawing step, removing from the inside wall of the pipeline matterprotruding into the space to be occupied by the liner.
 8. A method asdefined in claim 1, 2 or 3, wherein said liner material is high densitypolyethylene.
 9. A method as defined in claim 1, wherein the outsidediameter of said liner before radial expansion thereof is at least 94%of the inside diameter of the pipeline section.
 10. A method as definedin claim 1, wherein, for a given inside diameter of pipeline section,the outside diameter of said liner before radial expansion thereof is atleast 94% of said inside diameter in the case of an inside diameterbetween about 2 inches to about 4 inches, and increasing to about 96.5%of said inside diameter in the case of an inside diameter of about 10inches or greater.
 11. A method as defined in claim 1, wherein, for agiven inside diameter of pipeline section, the outside diameter of saidliner before radial expansion thereof is at least:(a) 94% of said insidediameter in the case of an inside diameter between about 2 inches toabout 4 inches; (b) 95% of said inside diameter in the case of an insidediameter of about 4 inches; (c) 96% of said inside diameter in the caseof an inside diameter between about 6 inches to about 8 inches; (d)96.5% of said inside diameter in the case of an inside diameter of about10 inches or greater.